Field of the Invention
The present invention relates to a fuel cell formed by stacking a membrane electrode assembly and separators. The membrane electrode assembly includes a pair of electrodes and an electrolyte membrane interposed between the electrodes.
Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs an electrolyte membrane. The electrolyte membrane is a polymer ion exchange membrane. In the fuel cell, the electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly is sandwiched between a pair of separators to form a unit cell (power generation cell). In use, in the fuel cell, generally, a predetermined number of unit cells are stacked together to form a fuel cell stack, e.g., mounted in a vehicle.
In the fuel cell, a fuel gas flow field is formed in a surface of one separator facing the anode for supplying a fuel gas to the anode, and an oxygen-containing gas flow field is formed in a surface of the other separator facing the cathode for supplying an oxygen-containing gas to the cathode. Further, a coolant flow field is formed between the adjacent separators of the fuel cells for supplying a coolant within electrode areas along surfaces of the separators.
Further, mostly, the fuel cell adopts so called internal manifold structure in which a fuel gas supply passage and a fuel gas discharge passage, an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage, and a coolant supply passage and a coolant discharge passage are formed in the fuel cell for allowing the fuel gas, the oxygen-containing gas, and the coolant to flow through the unit cells in the stacking direction.
However, in the internal manifold type fuel cell, it is difficult to uniformly supply reactant gases over the entire surfaces of reactant gas flow fields from reactant gas passages. In this regard, for example, a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2008-293743 is known.
The fuel cell is formed by stacking a membrane electrode assembly and separators. In the fuel cell, an electrolyte membrane is interposed between electrodes. The fuel cell has a reactant gas flow field for supplying reactant gases to electrode surfaces and reactant gas passages for allowing the reactant gases to flow in the stacking direction.
Each of the separators includes a substantially triangular inlet buffer having the width equal to the width of the reactant gas flow field and disposed on an inlet side of the reactant gas flow field. A portion of the reactant gas passage for supping the reactant gas is positioned adjacent to one ridge line of the inlet buffer. Further, the inlet buffer includes a plurality of protrusions. The density providing the protrusions is determined such that the protrusions are sparsely provided on the central side of the inlet buffer in comparison with the end side of the inlet buffer.
According to the disclosure, on the central side of the inlet buffer in the width direction where the reactant gas can flow smoothly, since the protrusions are sparsely provided, the flow rate of the reactant gas is low, and the reactant gas can be guided to the flow groves on the central side of the reactant gas flow field in the width direction.